507 research outputs found
On the problem of mass-dependence of the two-point function of the real scalar free massive field on the light cone
We investigate the generally assumed inconsistency in light cone quantum
field theory that the restriction of a massive, real, scalar, free field to the
nullplane is independent of mass \cite{LKS}, but the
restriction of the two-point function depends on it (see, e.g., \cite{NakYam77,
Yam97}). We resolve this inconsistency by showing that the two-point function
has no canonical restriction to in the sense of distribution theory.
Only the so-called tame restriction of the two-point function exists which we
have introduced in \cite{Ull04sub}. Furthermore, we show that this tame
restriction is indeed independent of mass. Hence the inconsistency appears only
by the erroneous assumption that the two-point function would have a
(canonical) restriction to .Comment: 10 pages, 2 figure
Gauged linear sigma model and pion-pion scattering
A simple gauged linear sigma model with several parameters to take the
symmetry breaking and the mass differences between the vector meson and the
axial vector meson into account is considered here as a possibly useful
template for the role of a light scalar in QCD as well as for (at a different
scale) an effective Higgs sector for some recently proposed walking technicolor
models. An analytic procedure is first developed for relating the Lagrangian
parameters to four well established (in the QCD application) experimental
inputs. One simple equation distinguishes three different cases:1. QCD with
axial vector particle heavier than vector particle, 2. possible technicolor
model with vector particle heavier than the axial vector one, 3. the unphysical
QCD case where both the KSRF and Weinberg relations hold. The model is applied
to the s-wave pion-pion scattering in QCD. Both the near threshold region and
(with an assumed unitarization) theglobal region up to about 800 MeV are
considered. It is noted that there is a little tension between the choice of
bare sigma mass parameter for describing these two regions. If a reasonable
globa fit is made, there is some loss of precision in the near threshold
region.Comment: 19 pages, 9 figure
Gauged Nambu-Jona-Lasinio model with extra dimensions
We investigate phase structure of the D (> 4)-dimensional gauged
Nambu-Jona-Lasinio (NJL) model with extra dimensions
compactified on TeV scale, based on the improved ladder Schwinger-Dyson (SD)
equation in the bulk. We assume that the bulk running gauge coupling in the SD
equation for the SU(N_c) gauge theory with N_f massless flavors is given by the
truncated Kaluza-Klein effective theory and hence has a nontrivial ultraviolet
fixed point (UVFP). We find the critical line in the parameter space of two
couplings, the gauge coupling and the four-fermion coupling, which is similar
to that of the gauged NJL model with fixed (walking) gauge coupling in four
dimensions. It is shown that in the presence of such walking gauge interactions
the four-fermion interactions become ``nontrivial'' even in higher dimensions,
similarly to the four-dimensional gauged NJL model. Such a nontriviality holds
only in the restricted region of the critical line (``nontrivial window'') with
the gauge coupling larger than a non-vanishing value (``marginal triviality
(MT)'' point), in contrast to the four-dimensional case where such a
nontriviality holds for all regions of the critical line except for the pure
NJL point. In the nontrivial window the renormalized effective potential yields
a nontrivial interaction which is conformal invariant. The exisitence of the
nontrivial window implies ``cutoff insensitivity'' of the physics prediction in
spite of the ultraviolet dominance of the dynamics. In the formal limit D -> 4,
the nontrivial window coincides with the known condition of the nontriviality
of the four-dimensional gauged NJL model, .Comment: 34 pages, 6 figures, references added, to appear in Phys.Rev.D. The
title is changed in PR
Cortical oscillatory dynamics and benzodiazepine-site modulation of tonic inhibition in fast spiking interneurons
Tonic conductance mediated by extrasynaptic GABAA receptors has been implicated in the modulation of network oscillatory activity. Using an in vitro brain slice to produce oscillatory activity and a kinetic model of GABAA receptor dynamics, we show that changes in tonic inhibitory input to fast spiking interneurons underlie benzodiazepine-site mediated modulation of neuronal network synchrony in rat primary motor cortex. We found that low concentrations (10 nM) of the benzodiazepine site agonist, zolpidem, reduced the power of pharmacologically-induced beta-frequency (15-30 Hz) oscillatory activity. By contrast, higher doses augmented beta power. Application of the antagonist, flumazenil, also increased beta power suggesting endogenous modulation of the benzodiazepine binding site. Voltage-clamp experiments revealed that pharmacologically-induced rhythmic inhibitory postsynaptic currents were reduced by 10 nM zolpidem, suggesting an action on inhibitory interneurons. Further voltage-clamp studies of fast spiking cells showed that 10 nM zolpidem augmented a tonic inhibitory GABAA receptor mediated current in fast spiking cells whilst higher concentrations of zolpidem reduced the tonic current. A kinetic model of zolpidem-sensitive GABAA receptors suggested that incubation with 10 nM zolpidem resulted in a high proportion of GABAA receptors locked in a kinetically slow desensitized state whilst 30 nM zolpidem favoured rapid transition into and out of desensitized states. This was confirmed experimentally using a challenge with saturating concentrations of GABA. Selective modulation of an interneuron-specific tonic current may underlie the reversal of cognitive and motor deficits afforded by low-dose zolpidem in neuropathological states
Noncommutativity from spectral flow
We investigate the transition from second to first order systems. This
transforms configuration space into phase space and hence introduces
noncommutativity in the former. Quantum mechanically, the transition may be
described in terms of spectral flow. Gaps in the energy or mass spectrum may
become large which effectively truncates the available state space. Using both
operator and path integral languages we explicitly discuss examples in quantum
mechanics, (light-front) quantum field theory and string theory.Comment: 31 pages, one Postscript figur
Conformal Phase Transition and Fate of the Hidden Local Symmetry in Large N_f QCD
It is observed that the Hidden Local Symmetry (HLS) for the vector mesons in
the ordinary QCD with smaller N_f plays the role of the "Higgsed magnetic gauge
symmetry" for the Seiberg duality in the SUSY QCD. For large N_f where the
conformal phase transition with chiral restoration and deconfinement is
expected to take place, we find that the HLS model also exhibits the chiral
restoration by the loop corrections (including the quadratic divergence) in a
manner similar to that in the CP^{N-1} model, provided that the bare HLS
Lagrangian respects the Georgi's vector limit at a certain N_f (\approx 7).Comment: 4 Pages (RevTeX), 3 PS figures are included Minor corrections are
made for the introductory part. This is the version to appear in Physical
Review Letter
Dynamical chiral symmetry breaking in gauge theories with extra dimensions
We investigate dynamical chiral symmetry breaking in vector-like gauge
theories in dimensions with () compactified extra dimensions, based on
the gap equation (Schwinger-Dyson equation) and the effective potential for the
bulk gauge theories within the improved ladder approximation. The non-local
gauge fixing method is adopted so as to keep the ladder approximation
consistent with the Ward-Takahashi identities.
Using the one-loop gauge coupling of the truncated KK
effective theory which has a nontrivial ultraviolet fixed point (UV-FP)
for the (dimensionless) bulk gauge coupling , we find that there
exists a critical number of flavors, ( for
for SU(3) gauge theory): For , the dynamical
chiral symmetry breaking takes place not only in the ``strong-coupling phase''
() but also in the ``weak-coupling phase'' ()
when the cutoff is large enough. For , on the other hand,
only the strong-coupling phase is a broken phase and we can formally define a
continuum (infinite cutoff) limit, so that the physics is insensitive to the
cutoff in this case.
We also perform a similar analysis using the one-loop ``effective gauge
coupling''. We find the turns out to be a value similar to
that of the case, notwithstanding the enhancement of the
coupling compared with that of the .Comment: REVTEX4, 38 pages, 18 figures. The abstract is shortened; version to
be published in Phys. Rev.
Dynamical Generation of CKM Mixings by Broken Horizontal Gauge Interactions
The fermion mass matrices are calculated in the framework of the dynamical
mass generation by the broken horizontal gauge interactions. The
non-proportional mass spectra between up- and down-sectors and CKM mixings are
obtained solely by radiative corrections due to the ordinary gauge
interactions.Comment: 20 pages + 1 uuencoded eps figure, PHYZZ
NAMBU-GOLDSTONE BOSON ON THE LIGHT-FRONT
Spontaneous breakdown of the continuous symmetry is studied in the framework
of discretized light-front quantization. We consider linear sigma model in 3+1
dimensions and show that the careful treatment of zero modes together with the
regularization of the theory by introducing NG boson mass leads to the correct
description of Nambu-Goldstone phase on the light-front.Comment: To appear in the proceedings of the 13th Symposium on Theoretical
Physics, Mt. Sorak, Korea, from 27 June to 2 July, 1994
Chiral Dynamics and Fermion Mass Generation in Three Dimensional Gauge Theory
We examine the possibility of fermion mass generation in 2+1- dimensional
gauge theory from the current algebra point of view.In our approach the
critical behavior is governed by the fluctuations of pions which are the
Goldstone bosons for chiral symmetry breaking. Our analysis supports the
existence of an upper critical number of Fermion flavors and exhibits the
explicit form of the gap equation as well as the form of the critical exponent
for the inverse correlation lenght of the order parameterComment: Latex,10 pages,DFUPG 70/9
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